Rain Water Harvesting Manual For Urban Areas | Rain Water Harvesting System

Harvesting System Broadly rainwater can be harvested for two purposes Storing rainwater for ready use in containers above or below ground Charged into the soil for withdrawal later (groundwater recharging)

Source: A Water Harvesting Manual For Urban Areas From where to harvest rain

Rainwater harvesting can be harvested from the following surfaces

Rooftops: If buildings with impervious roofs are already in place, the
catchment area is effectively available free of charge and they provide a
supply at the point of consumption. Paved and unpaved areas i.e.,
landscapes, open fields, parks, stormwater drains, roads and pavements
and other open areas can be effectively used to harvest the runoff. The
main advantage in using ground as collecting surface is that water can
be collected from a larger area. This is particularly advantageous in
areas of low rainfall.

Waterbodies: The potential of
lakes, tanks and ponds to store rainwater is immense. The harvested
rainwater can not only be used to meet water requirements of the city,
it also recharges groundwater aquifers. Stormwater drains: Most of
the residential colonies have proper network of stormwater drains. If
maintained neatly, these offer a simple and cost effective means for
harvesting rainwater.

Whether to store rainwater or use it for recharge:

The decision whether to store or recharge water depends on the rainfall
pattern and the potential to do so, in a particular region. The
sub-surface geology also plays an important role in making this
decision.

For example, Delhi, Rajasthan and Gujarat where the
total annual rainfall occurs during 3 or 4 months, are examples of
places where groundwater recharge is usually practiced. In places like
Kerala, Mizoram, Tamil Nadu and Bangalore where rain falls throughout
the year barring a few dry periods, one can depend on a small sized tank
for storing rainwater, since the period between two spells of rain is
short. Wherever sub-strata is impermeable recharging will not be
feasible. Hence, it would be ideal to opt for storage.

Source: A Water Harvesting Manual For Urban Areas In places where the groundwater is saline or not of potable standards, the alternate system could be that of storing rainwater.

Beyond generalisations, it is the requirement that governs the choice
of water harvesting technique. For example, in Ahemadabad, which has
limited number of rainy days as that of Delhi, traditional rainwater
harvesting tanks, known as tankas, are used to store rainwater even
today in residential areas, temples and hotels.